This invention relates to a process for preparing overcoated electrophotographic imaging members and more particularly, to a process of preparing electrophotographic imaging members overcoated with a solid reaction product of a cross-linkable organosiloxane colloidal silica hybrid polymer and an ammonium salt of an alkoxy silane.
The formation and development of electrostatic latent images utilizing electrophotographic imaging members is well known. One of the most widely used processes being xerography as described by Carlson in U.S. Pat. No. 2,297,691. In this process, an electrostatic latent image formed on an electrophotographic imaging member is developed by applying electropscopic toner particles thereto to form a visible toner image corresponding to the electrostatic latent image. Development may be effected by numerous known techniques including cascade development, powder cloud development, magnetic brush development, liquid development and the like. The deposited toner image is normally transferred to a receiving member such as paper.
Electrophotographic imaging systems may utilize single multilayered organic or inorganic photoresponsive devices. In one photoresponsive device, a substrate is overcoated with a hole injecting layer and a hole transport layer. These devices have been found to be very useful in imaging systems. The details of this type of overcoated photoreceptor are fully disclosed, for example, in U.S. Pat. No. 4,265,990. The entire disclosure of this patent is incorporated herein by reference. If desired, multilayered photoresponsive devices may be overcoated with a protective layer. Other photoreceptors that may utilize protective overcoatings include inorganic photoreceptors such as the selenium alloy photoreceptors, disclosed in U.S. Pat. No. 3,312,548, the entire disclosure of which is incorporated herein by reference.
When utilizing such an organic or inorganic photoresponsive device in different imaging systems, various environmental conditions detrimental to the performance and life of the photoreceptor from both a physical and chemical contamination viewpoint can be encountered. For example, organic amines, mercury vapor, human fingerprints, high temperatures and the like can cause crystallization of amorphous selenium photoreceptors thereby resulting in undesirable copy quality and image deletion. Further, physical damage such as scratches on both organic and inorganic photoresponsive devices can result in unwanted printout on the final copy. In addition, organic photoresponsive devices sensitive to oxidation amplified by electric charging devices can experience reduced useful life in a machine environment. Also, with certain overcoated organic photoreceptors, difficulties have been encountered with regard to the formation and transfer of developed toner images. For example, toner materials often do not release sufficiently from a photoresponsive surface during transfer or cleaning thereby forming unwanted residual toner particles thereon. These unwanted toner particles are subsequently embedded into or transferred from the imaging surface in subsequent imaging steps, thereby resulting in undesirable images of low quality and/or high background. In some instances, the dry toner particles also adhere to the imaging member and cause printout of background areas due to the adhesive attraction of the toner particles to the photoreceptors surface. This can be particularly troublesome when elastomeric polymers or resins are employed as photoreceptor overcoatings. For example, low molecular weight silicone components in protective overcoatings can migrate to the outer surface of the overcoating and act as an adhesive for dry toner particles brought into contact therewith in the background areas of the photoreceptor during xerographic development. These toner deposits result in high background prints.
When highly electrically insulating polysiloxane resin protective overcoatings are used on photoreceptors, the thickness of the overcoatings are limited to extremely thin layers due to the undesirable residual voltage cycle up. Thin overcoatings provide less protection against abrasion and therefore fail to extend photoreceptor life for any significant period. Conductive overcoating components permit thicker coatings but can cause fluctuations in electrical properties with change in ambient humidity and also contribute to lateral conduction with a resulting reduction in image resolution. Moreover, under cycling conditions over an extended period of time at elevated temperatures and high relative humidity, such silicone overcoated photoreceptors containing a conductive overcoating component can cause deletions in the images of final copies.